Mechanical warewashing machines have been common in the institutional and household environments for many years. Such automatic warewashing machines clean dishes using two or more cycles which can include initially a wash cycle followed by a rinse cycle. Such dishwashers can also utilize soak cycle, prewash cycle, scrape cycle, second wash cycle, a rinse cycle, a sanitizing cycle and a drying cycle, if required. Such cycles can be repeated if needed and additional cycles can be used. After passing through a wash, rinse and dry cycle, dishware, cups, glasses, etc., can exhibit spotting that arises from the uneven draining of the water from the surface of the ware after the rinse step. Spotting is aesthetically unacceptable in most consumer and institutional environments.
In order to substantially prevent the formation of spotting rinse agents have commonly been added to water to form an aqueous rinse which is sprayed on the dishware after cleaning is complete. The precise mechanism through which rinse agents work is not established. One theory holds that the surfactant in the rinse aid is absorbed on the surface at temperatures at or above its cloud point, and thereby reduces the solid-liquid interfacial energy and contact angle. This leads to the formation of a continuous sheet which drains evenly from the surface and minimizes the formation of spots. Generally, high foaming surfactants have cloud points above the temperature of the rinse water, and, according to this theory, would not promote sheet formation, thereby resulting in spots. Moreover, high foaming materials are known to interfere with the operation of the warewashing machine. Common rinse aid formulas are used in an amount of less than about 1,000 parts preferably less than 500 parts, commonly 50 to 200 parts per million of active materials in the aqueous rinse. Rinse agents available in the consumer and institutional markets comprise liquid or solid forms which are typically added to, dispersed or dissolved in water to form an aqueous rinse. Such dissolution can occur from a rinse agent installed onto the dish rack. The rinse agent can be diluted and dispensed from a dispenser mounted on or in the machine or from a separate dispenser that is mounted separately but cooperatively with the dish machine.
Commonly available commercial rinse agents typically comprise a low foaming surface active agent made from homopolymers or copolymers of an alkylene oxide such as ethylene oxide or propylene oxide or mixtures thereof. Typically, the surfactants are formed by reacting an alcohol, a glycol, a carboxylic acid, an amine or a substituted phenol with various proportions and combinations of ethylene oxide and propylene oxide to form both random and block copolymer substituents.
The commonly available rinse agents have primarily focused on reducing spotting and filming on surfaces such as glass, ceramics, china and metal. However, plastic dishware is more commonly used now, especially in the institutional market. A special problem for rinse aid surfactants used for plasticware is the attack and crazing of the ware. Block copolymer surfactants do not seem to attack plastics as strongly as fatty alcohol or alkyl phenol-based nonionic surfactants. Linear alkoxylates show they do not attack plexiglass, polystyrene, or Tupperware.RTM., common utensil plastics. Nevertheless, current surfactants have not provided the desired sheeting in an acceptable drying time following the rinse cycle.
U.S. Pat. No. 5,298,289 describes the treatment and after-treatment of surfaces, especially metals, with derivatives of polyphenol compounds. These compositions are also said to be useful in treating plastic and painted surfaces to improve rinsability without water breaks. The surfactants employed are a combination of previously known anionic and nonionic surfactants.
Liquid dishwashing detergent compositions are described in U.S. Pat. No. 4,492,646 containing highly ethoxylated nonionic surfactants to reduce spotting and filming on surfaces such as glass, ceramics and metal.
European Patent Publication 0,432,836 describes the use of alkyl polyglycoside surfactants in rinse aid compositions on polycarbonate.
Fluorinated surfactants are described in U.S. Pat. No. 4,089,804 where a non-ethoxylated fluoroaliphatic sulfonamide alcohol is added to typical fluorinated hydrocarbon surfactants as a synergist. The compositions are described as useful in a wide variety of industries, e.g., household cosmetic and personal products. Rinse aid for dishwashing is mentioned.
Organosilanes are described in rinse aid compositions where the organosilane contains either a nitrogen, phosphorous or sulfur cationic group in combination with an anion, e.g. a monofunctional organic acid. U.S. Pat. No. 4,005,024 describes such compounds in a rinse aid composition to attract specific soil particles.
Aminosilanes have been described with a low foaming ethoxylated nonionic surfactant in rinse aid compositions in automatic dishwashing machines.
None of the fluorinated surfactants or silanes described in rinse aid compositions have focused on their use in plasticware.
Surprisingly, we have found that by adding a combination of a fluorinated hydrocarbon surfactant, especially an ethoxylated fluorinated aliphatic sulfonamide alcohol, with a silane surfactant, e.g. a polyalkylene oxide-modified polydimethylsiloxane, to a conventional rinse aid composition containing hydrocarbon surfactants, the resulting rinse agent provides excellent sheeting properties on plasticware without attacking or crazing the plastic and, more importantly, providing dried, non-spotted plasticware in acceptable time following the rinse cycle.